1. Field of the Invention
The present invention relates to a circuit for bypassing the Zener diodes connected across a DC brush motor to control the speed of the motor when the motor moves in reverse under the force of a bias device such as a spring.
2. Description of Co-pending Applications
In a co-pending patent application of Christopher M. Lange entitled xe2x80x9cDrive Circuit and Method for an Electric Actuator with Spring Returnxe2x80x9d Ser. No. 08/904,005, filed Jul. 13, 1997, now Pat. No. 6,249,100 and assigned to the assignee of the present invention, an actuator system is shown in which an output shaft is positioned by a spring in a first position and upon command, is driven through a gear train to a second position by an electric motor. The circuit includes an input circuit for providing a current large enough to rotate the shaft against the force of the spring. A rotation sensor produces a signal when the motor and shaft are stalled at the second position and a modulation circuit receiving the signal from the rotation sensor operates to reduce the current to the motor so as to hold the stalled shaft and motor at the second position with a minimum of energy usage. When the current to the motor is removed, the spring forces the motor in reverse and the shaft returns to the first position. A Zener diode and a conventional diode are connected in series, between the power terminals of the motor to provide a current circulation path which regulates the voltage induced across the windings of the motor and enhances the braking effect provided by the motor in its unenergized state when it is rotating in reverse under the force of the bias. Unfortunately, during powered operation, when the motor is driving the shaft toward the second position, the current passes through the Zener diode causing extra power consumption and reducing the efficiency rate.
In a co-pending application of Christopher M. Lange and Greg T. Mrozek entitled xe2x80x9cCircuit using Current Limiting to Reduce Power Consumption of Actuator with DC Brush Motorxe2x80x9d Ser. No. 09/717/564, Filed Nov. 21, 2000, and assigned to the assignee of the present invention, an improvement to the circuit of the above mentioned application Ser. No. 08/904,005 is described and claimed. In the improved circuit, a Zener diode bypass circuit is briefly described which comprised the subject matter of the present invention.
The present invention overcomes the problem of wasted energy passing through the Zener diode(s) during forward operation by providing a bypass circuit that is activated to bypass the Zener diode(s) during forward operation.